Fix BFLA (Broken Function Level Authorization) in Polka

BFLA (Broken Function Level Authorization) in Polka occurs when administrative or sensitive endpoints are exposed without explicit permission checks. Attackers exploit this by guessing or discovering high-privilege URLs and executing actions they aren't authorized for. In minimalist frameworks like Polka, security isn't 'magic'—if you don't middleware-gate it, it's public.

The Vulnerable Pattern

const polka = require('polka');
const app = polka();
// VULNERABLE: No authorization check.
// Any user knowing the ID can delete others.
app.delete(‘/api/users/:id’, (req, res) => {
const { id } = req.params;
db.users.remove(id);
res.end(User ${id} deleted);
});
app.listen(3000);

The Secure Implementation

The fix involves moving from 'security by obscurity' to explicit 'Role-Based Access Control' (RBAC). By implementing a higher-order function as middleware (authorize), we intercept the request before it reaches the sensitive business logic. The middleware validates the user's claims (extracted from a JWT or session) against the required role for that specific function. If the criteria aren't met, the request is short-circuited with a 403 Forbidden status, preventing unauthorized execution of the function.

const polka = require('polka');
const app = polka();
// Middleware to enforce Function Level Authorization
const authorize = (role) => (req, res, next) => {
const user = req.user; // Populated by an earlier auth middleware
if (user && user.role === role) {
next();
} else {
res.statusCode = 403;
res.end(‘Forbidden: Insufficient permissions’);
}
};
// SECURE: Only users with ‘admin’ role can hit this function
app.delete(‘/api/users/:id’, authorize(‘admin’), (req, res) => {
const { id } = req.params;
db.users.remove(id);
res.end(User ${id} deleted by admin);
});
app.listen(3000);